When should an American president issue a pardon to a convicted criminal?

Will President Bush step in to keep Scooter Libby out of jail?

For supporters of former White House aide Lewis "Scooter" Libby, who faces 30 months in jail for perjury and obstruction of justice, the answer is "right now".

They believe Libby is a loyal public servant who has been treated as a scapegoat for the administration and have called on President George W Bush to spare him a prison term.

For others, the idea that Libby would be granted a pardon is political cronyism that goes against the very principle of how the power should be used.

The question has become all the more urgent since Libby's lawyers failed to persuade District Judge Reggie Walton not to send him to jail before his appeal is heard, meaning he could start his sentence within weeks.

Experts agree that no matter how much Mr Bush may want to help his vice-president's former chief-of-staff, granting a pardon right now - if Libby were to apply - would be politically risky.

"Bush is perfectly capable of pardoning Libby tomorrow but my guess is he won't and that he will wait until after the 2008 election," says Professor Garrett Epps, of the University of Oregon School of Law.

"Presidents will sometimes issue pardons when there's no political price for them to pay, because they are leaving office."

Mr Bush's other options would be to commute the sentence so Libby serves a lesser term, or do nothing and leave it for his successor to decide.

Past scandals

If Mr Bush were to wait for the final hours of his presidency to act, he would not be the first - but the suggestion recalls past scandals.

Bill Clinton issued 140 pardons on his last day as US president

On the very last day of his presidency, Bill Clinton issued pardons for 140 people, including his brother Roger Clinton and former business partner Susan McDougal, who had been jailed for refusing to give evidence against the Clintons in the Whitewater real estate scandal.

Even more controversial was the pardon for financier Marc Rich, who faced more than 50 charges of tax evasion and illegal oil trading - and for whom Libby, coincidentally, had worked as a lawyer.

When it was revealed that Mr Rich's ex-wife had made large donations to Mr Clinton's presidential library fund, the outcry was such that a congressional inquiry into Mr Clinton's final pardons was set up.

Mr Clinton later said the gifts had nothing to do with his clemency but admitted it had been "terrible politics".

President George H W Bush, the current president's father, also issued controversial pardons to Reagan administration officials charged for their role in the Iran-Contra affair.

'Stingy' pardoner

Meanwhile, George W Bush seems remarkably unwilling to exercise his sovereign prerogative to pardon even in unremarkable cases.

George W Bush has issued fewer pardons than his predecessors

Margaret Colgate Love, who was the Department of Justice's Pardon Attorney from 1990 to 1997 and testified at the hearing on Mr Clinton's final pardons, says Mr Bush has been "stingy" in his use of a power historically seen as a presidential duty.

Mr Bush has pardoned only 113 people out of more than 1,000 applications in six years in office and has commuted only three sentences, turning down 5,000 requests.

By comparison, Ronald Reagan had pardoned 300 people by the equivalent point in his presidency and commuted 13 sentences. In total, Richard Nixon issued 863 pardons and commuted the sentences of 60 people.

Most pardons are issued to ordinary people who have served their term, become exemplary members of society and want their civil rights restored so they can vote and serve on a jury. The other function of pardons is to redress sentences seen as excessively harsh.

For Ms Love, who now represents clients seeking pardons, the key to whether Mr Bush could pardon Libby - or at least commute his sentence - without provoking a storm lies in whether he starts to pardon the hundreds of ordinary people who have been waiting in line for years.

"If the president were to take his pardon power seriously and start working to reduce his caseload, and try to get some rhyme and reason about what he is doing, then he could fit the Scooter Libby pardon into that territory," she says.

Conservative desire

In the short term, whether or not Libby escapes jail may boil down to how much Mr Bush - whose powers of pardon in federal cases are, after all, unlimited - really wants to do for him.

PARDONS GRANTED

George W Bush - 113 (to date)

Bill Clinton - 396

George HW Bush - 74

Ronald Reagan - 393

Jimmy Carter - 534

Gerald Ford - 382

Richard Nixon - 863

Lyndon Johnson - 960

John F Kennedy - 472

From the Office of the Pardon Attorney, as of 4 June 2007

So far Mr Bush has seemed keen to distance himself from Libby's case, saying the legal process must first run its course, says Professor Brian Kalt of the University of Michigan.

"There are a lot of conservatives who would like the president to pardon Libby and that really is at this point the only thing that can save him, other than some issue on appeal," he says.

But, he points out, despite his reputation for loyalty Mr Bush has yet to pardon anyone close to him. "At this point it's hard to see what he would gain by sticking his neck out like that."

Professor Calvin Massey, of the University of California's Hastings College of the Law, also believes Mr Bush is unlikely to act immediately.

"The president is probably hoping that Libby remains free pending the outcome of his appeal. Then he might pardon him in the dying days of his administration."

Prudent president

And if Mr Bush does not come good, should Libby pin his hopes on the new man, or woman, in the White House in 2009?

When Republican candidates for the 2008 elections were asked whether they would pardon Libby, only two said they definitely would. Neither of those are among the frontrunners.

While former New York Mayor Rudy Giuliani said he believed the sentence was "way out of line", he said he would wait for the appeals process to play out before deciding on a pardon. Former Massachusetts Governor Mitt Romney and Arizona Senator John McCain were similarly non-committal.

Professor Epps believes they are right to be cautious.

He gives the example of President Gerald Ford, who pardoned his predecessor Richard Nixon to prevent him being charged over the Watergate scandal, and in so doing may have cost himself re-election.

"If a pardon application were to arrive on a new president's desk, I think that would be something they would want to avoid," Professor Epps says.

"A prudent president would not want to start his term by pardoning someone who is convicted of a felony."